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Study On Preparation And Catalytic Performances Of A Novel Tungstophosphoric Acid-based Solid Acid

Posted on:2019-01-12Degree:MasterType:Thesis
Country:ChinaCandidate:G Q TangFull Text:PDF
GTID:2321330548962324Subject:Industrial Catalysis
Abstract/Summary:PDF Full Text Request
It has the following advantages when solid acid was selected as catalyst for the production of biodiesel via esterification reaction of oleic acid and methanol with the employing of chemical acid-base catalysis methods,such as the disadvantages that the traditional liquid acid-base catalyzed process is complex and easy to produce a large amount of salty wastewater can be overcomed;simple separation and recycle;the quality requirements of the raw material oil are low,and the esterification and transesterification reactions can be catalyzed at the same time.In this study,H3PW12O40?tungstophosphoric acid?was applied as matrix,and which was undergone a series of modifications and loading to obtain a Br?nsted-Lewis acid-based solid acid catalyst with high catalytic activity and stability.1.The structure of PW12 in the H3PW12O400 will be converted to other types of PWn anion with the changing of solution pH environment,and then the F-can be combined with the newly formed PWn structure through the strong electronegativity.Based on this above considering,a series of solid acid catalysts[H4PW12O40]F-N?N=1.5,3,5,N is pH value of the solution?was synthesized by hydrothermal method;the specific surface area and surface acidity of the heteropoly acid are closely related to the diameter of the cation responsible for the counter ion in its molecular structure,and considering that the modification effect has a certain influence relationship with the preparation method,so the common impregnation method,sol-gel method and the ultrasonic impregnation method are respectively adopted when La3+was used to modify H3PW12O40.As a result,three solid acid catalysts LaPW12O40-1,LaPW12O40/SiO2 and LaPW12O40-2 were synthesized;an active surface with special functional groups can be formed from the sidewalls modification of single-wall carbon nanotubes?SWCNTs?.Thus,LaPxSi?1-x?W12O40/SWCNTs catalysts are synthesized from the sidewall modification and La3+modification of SWCNTs through sol-gel method with the employing of SWCNTs as carrier.2.The catalytic activities and stabilities of them were compared when they were used for the catalytic synthesis of biodiesel from the esterification reaction of oleic acid and methanol,respectively.The effects of different catalyst dosage,reaction temperature and molar ratio of methanol to oleic acid on the conversion of oleic acid were studied.Results showed that[H4PW12O40]F-3 had the highest catalytic activity in[H4PW12O40]F-N?N=1.5,3,5?,and the conversion of oleic acid can be high to 88.94%when the molar ratio of methanol to oleic acid was 14:1,mass ratio of catalyst to reactants was 2.5%,reaction temperature was 65?and reaction time was 1 h;LaPW12O40/SiO2 has the highest catalytic activity in the LaPW12O40-1?LaPW12O40/SiO2 and LaPW12O40-2,and the conversion of oleic acid can be high to 93%when the molar ratio of methanol to oleic acid was 8:1,mass ratio of catalyst to reactants was 2%,reaction temperature was 65?and reaction time was 1 h;When LaPxSi?1-x?W12O40/SWCNTs was used as catalyst,the conversion rate of oleic acid was81.2%after 1 hour of reaction at 65?and the molar ratio of alcohol to oil was 15:1,the amount of catalyst was 1.5%.It can be concluded that the LaPW12O40/SiO2 has highest catalytic activity,which can be explained as follows:a SiO2 network was formed from the hydrolytic action of Si?OC2H5?4?TEOS?under acidic conditions via Sol-Gel process.The H+of H3PW12O40 will bond with Si-OH in SiO2 network to form a(?Si-OH2+)(H2PW12O-40)complex with strong electrostatic adsorption force,thus promoting the adsorption of La3+on the surface of SiO2,then formed Lewis site acid.This make LaPW12O40/SiO2 was a solid acid of Br?nsted-Lewis acid.3.the kinetic simulation of the esterification of oleic acid and methanol was carried out with[H4PW12O40]F-3 as a catalyst.The effects of the reaction temperature,the ratio of alcohol and oil and the amount of the catalyst on the esterification of oleic acid were discussed.By eliminating the influence of external diffusion and internal diffusion of reaction,the mechanism of reaction is identified as Rideal mechanism.The Rideal activation mechanism is used to calculate the apparent activation energy of Ea=62.45kJ/mol,and the pre factor A=5.77×107L·mol-1·min-1.Based on these above studies,it can be known that the Lewis acid property of phosphotungstic acid can be changed,and its catalytic activity and stability can be improved when different modification or loading methods were used to synthesize a new type of solid acid catalyst with the employing of H3PW12O400 as substrate.The lossing of its acidic active sites can be reduced when it was used in catalyzing esterification reaction of oleic acid and methanol.The modified phosphotungstic acid catalyst can be expected to be a novel catalyst with high catalytic activity and stability for biodiesel production by esterification of oleic acid and methanol.
Keywords/Search Tags:SWCNTs, Biodiesel, Phosphotungstic acid, Br?nsted acid, Lewis acid
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